1. Field of the Invention
The present invention relates generally to gas distribution plates utilized in semiconductor wafer processing equipment, and more particularly to a liquid cooled gas distribution plate for use in a chemical vapor deposition chamber.
2. Background of the Related Art
Gas distribution plates are commonly utilized in chemical vapor deposition (CVD) chambers to distribute gases uniformly as they are introduced into the chamber. Uniform gas distribution is necessary to achieve uniform deposition characteristics upon the surface of a wafer located within the chamber.
Problems have arisen in utilizing the currently available gas distribution plates when the temperature of the plate causes problems in handling a gas or gas mixture, such as unwanted reactions between components of the deposition gas. Thermal management of the deposition gas may be necessary or desirable in any process that utilizes gases, including TEOS, silane, tungsten, tungsten silicide, titanium nitride, aluminum, copper, titanium, sub-atmospheric CVD processes and the like.
For example, to deposit a layer of tungsten silicide by chemical vapor deposition, tungsten hexafluoride and silane, are input through a gas manifold and mixed in a water cooled gas mixing chamber within the gas manifold head. The two reactant gases must be kept cool, because the two gases will react to form a solid, tungsten silicide, at temperatures greater than approximately 25 degrees centigrade. After mixing the reactant gases in the cooled gas manifold head, the gaseous mixture is passed through a standard gas distribution plate system, whereby a uniform distribution of the gaseous mixture is introduced into the deposition chamber. The gaseous mixture then impinges upon a wafer within the chamber, whereupon the two gases react to deposit tungsten silicide on the wafer.
Particulate contamination problems have occurred in the above described systems when the prior art gas distribution plate has warmed to temperatures greater than 25 degrees centigrade. When such plate warming occurs, the two gases react at the gas distribution plate to form large particulates that can contaminate the wafer. Furthermore, at temperatures greater than about 25 degrees centigrade, deposits may form and clog the gas distribution holes of the plate to cause uneven deposition. Additionally, a layer of tungsten silicide may form on the inner surface of the plate and later flake off in large particulates which rain down upon the wafer to create an uneven tungsten silicide layer, whereby the wafer is contaminated and rendered valueless.
FIG. 1 is a perspective view of a system 10 including a pumping plate or lid 11 for a commercially available chemical vapor deposition chamber. The pumping plate 11 includes a gas injection manifold 12 and a gas box 14. The gas injection manifold 12 typically includes a gas input manifold 16 which communicates with a gas source, a gas output manifold 18 which communicates with the gas box 14, and a constant voltage gradient gas feedthrough 20 disposed therebetween.
FIG. 2 is an exploded view of the gas box 14 of FIG. 1 which is RF hot and routes process gas from the gas output manifold 18 to the blocker plate 22. The blocker plate 22, in turn, channels process gas to the gas distribution plate 24 where the gases are evenly distributed over the wafer through hundreds of holes. An isolator 26 is disposed between the "RF hot" gas distribution plate 24 and the "electrically grounded" chamber lid 11.
FIG. 3 is a cross-sectional view of the gas injection manifold 12 shown in FIG. 1 that channels process gases from the chamber body gas feedthrough line (not shown) into the gas box 14 (See FIG. 2). The gas injection manifold 12 generally comprises a gas input manifold 16, a gas output manifold 18 and a constant voltage gradient feedthrough 20 disposed therebetween. The gas input manifold 16 and the gas output manifold 18 are typically made of a metal, whereas the constant voltage gradient feedthrough 20 includes an electrically insulative housing 22, such as quartz or polytetrafluoroethylene (PTFE, available under the trademark TEFLON from DuPont de Nemour & Company of Wilmington, Del. Gas feed tubes 24 extend from the gas input manifold 16, through the constant voltage feedthrough 20, to the gas output manifold 18. A ceramic resistor tube 26 is disposed around the gas feed tubes 24 to provide the constant voltage gradient between the RF hot gas output manifold 18 and the electrically grounded gas input manifold 16.
The electrically insulative housing 22 is also provided with a pair of water-carrying channels or passages 28 adjacent the passages 30 which receive the gas feed tubes 24. The water-carrying channels 28 include a water input channel and a water output channel for transporting water to and from the gas input manifold 16 and a coolant pool or channel (not shown) within the chamber lid assembly 10. The coolant pool or channel allows water to heat or cool various parts of the lid assembly 10. Furthermore, water passing through the water-carrying channels 28 may be used to provide thermal management of gases passing through the gas feed tubes 24. Typically, water will be withdrawn through the water output channel and recycled to a heat exchange system (not shown) that controls the temperature of the water.
FIG. 4 is a gas delivery system that incorporates the gas injection manifold 12 of FIG. 3. The reactant gases are passed through the gas input manifold 16, the gas feed tube(s) 24 of the constant voltage gradient feedthrough 20 and the gas output manifold 18 before being released into the gas box 14 of the chemical vapor deposition chamber. The gases are cooled by passing a liquid coolant through the gas input manifold 16, a first liquid channel 28 of the feedthrough 20, the gas output manifold 18 and into the liquid coolant pool 32 adjacent the gas box 14 before returning the liquid through the gas output manifold 18, a second liquid channel 28 of the feedthrough 20, and the gas input manifold 16. The coolant liquid exiting the gas input manifold 16 may be returned to a central or dedicated heat exchange system or passed to another device or chamber for further cooling.
However, the system described above in reference to FIGS. 1-4 suffers from several operational limitations. First, it is necessary to clean the gas passageways of the gas injection manifold 12 periodically due to the buildup of particulate contaminants therein. To facilitate thorough cleaning, the gas injection manifold must be disassembled. However, when the electrically insulative housing 20 is loosened and removed from the gas input and output manifolds 16, 18, the water-carrying passageways 28 are consequently opened, thereby allowing water to spill on or around the equipment. While it may be possible to minimize the amount of water spilled by evacuating the water channels 28 prior to disassembly, these measures are wholly unproductive because the water channels do not typically require cleaning. Furthermore, the seals between the reassembled housing 20 and gas input and output manifolds 16, 18 that communicate with the water channels 20 must be checked for leaks following the maintenance procedure.
Another limitation of the prior art arrangement is that the electrically insulating housing, ceramic resistors and feed tubes are typically made from materials having low thermal conductivities. Consequently, the transfer of thermal energy between fluids is quite low.
Furthermore, passing the heat exchange fluid through the electrically insulative housing imposes certain constraints on the diameter of the water-carrying channels and, therefore, the water flow rate and pressure drop through the system.
FIG. 5 is an alternative heat exchange system 40 which overcomes several of the limitations stated above with regard to system 10 by providing flexible water coolant fluid tubes 42, 44 directly to and from the coolant pool 32. However, this alternative system 40 does not allow for thermal management of the gas injection manifold 16 and, therefore, is not suitable for use with certain processes, such as deposition of tungsten silicide as described above.
Therefore, there is a need for a chemical vapor deposition chamber having improved thermal management over the gas injection manifold and gas box. There is also a need for a gas injection manifold providing improved heat exchange between a heat exchange fluid and the process gases entering the chamber. It would be desirable if the gas injection manifold allowed the water cooling system to remain closed during maintenance and cleaning of the manifold, thereby simplifying the cleaning procedure and avoiding spills. It would be further desirable if the system allowed higher water flow rates and a lower pressure drop across the chamber.